Primer coatings, or primers for short, are the collective designation for thin coats applied directly to a metal substrate in order, within a coating system, to take on a particular function as primers, especially for promoting adhesion and controlling corrosion (cf. Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, “primers”).
Primer-surfacers, or “surfacing primers”, are undercoating materials which combine the properties of primers and surfacers (cf. Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, “primer-surfacers”).
Priming materials, including the materials for intermediate coatings, are coating materials which are applied directly to a substrate or to an existing coating for refinishing purposes. They include, in particular, primer-surfacers, primers, surfacers, and putties (cf. Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, “priming materials”).
Surfacers are coating materials for intermediate coating in automotive OEM finishing, automotive refinish, and industrial coating. Their function is to compensate unevennesses in the substrate, assist adhesion and corrosion control (particularly as primer-surfacers), and to ensure effective stonechip resistance in the coating system as a whole or in the multicoat paint system (cf. Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, “surfacers”, or Goldschmidt/Streitberger, BASF Handbuch Lackiertechnik, Vincentz Verlag, Hannover, 2002, “7.1.4 Surfacers”, pages 725 to 728, and “7.2 Automotive refinish”, pages 737 to 744).
Putties or filling compounds according to DIN 55945:1996-09 are pigmented, highly filled coating materials which are used for compensating substrate unevennesses which are too great to be remedied by primers or surfacers (cf. Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, “putties”; or Goldschmidt/Streitberger, BASF Handbuch Lackiertechnik, Vincentz Verlag, Hannover, 2002, “7.2 Automotive refinish”, pages 737 to 744).
The corrosion inhibition effect of the coatings described above derives in particular from the presence therein of anticorrosive pigments (cf. Römpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag, Stuttgart, New York, 1998, “anticorrosive coating material” and “anticorrosive pigments”). A particularly high corrosion control effect is displayed by chromate and/or zinc anticorrosive pigments (cf.op. cit., “chromate pigments”, “zinc chromates”, “zinc oxide”, “zinc phosphate ”, and “zinc pigments”, and also German patent application DE 100 48 268 A1). These pigments, however, are very objectionable toxicologically, which is why the art sector has endeavored to replace them by other, toxicologically less objectionable or unobjectionable anticorrosive pigments.
Chromium- and zinc-free anticorrosive pigments are conventional.
For instance, the company Heubach GmbH sells unhydrated calcium hydrogen phosphate under the brand name Heucophos® CHP as an anticorrosive pigment for water-thinnable hybrid systems.
The company Lawrence Industries sells calcium borosilicates, particularly Halox® CW-2230, esters, oils, phenolic resins, alkyd/chlorinated rubber, and VT alkyd resins.
The company Grace sells amorphous, calcium-modified silicon dioxide under the brand name Shieldex® AC-3 as a nontoxic anticorrosive pigment for coil-coating primers and 1- or 2-component wash primers.
The company Heubach also sells the zinc salt of an organic nitro compound (zinc content: 44% by weight) under the brand name Heucorin® RZ as a corrosion inhibitor for coatings.
It has been found, however, that none of these anticorrosive pigments and none of the inhibitors has on its own a corrosion control effect sufficient to meet the stringent requirements imposed on the priming materials for automotive refinish. Moreover, the priming materials in question, and the prime coats and intermediate coatings produced from them, leave something to be desired in their substrate adhesion and intercoat adhesion and also in their stonechip protection effect.